Particularly in boating and other nautical applications, it is frequently necessary to grip a tensioned line for periods of time. (The nautical term “line” will be used throughout to refer to the various types of flexible ropes usually suitable for manual handling.) The device used to retain tension in a line is called a cleat. A cleat should hold or grip the line securely and at the same time permit the line to be easily attached to and removed from the cleat.
Cleats of various types have been used for literally centuries. Simple cleats are mounted on a dock and have horizontally projecting arms or bars, around which a line used as a painter for mooring a boat, can be wrapped. Such cleats can hold lines securely, but attaching line to and removing lines from them takes time.
A cam cleat is another type of cleat more often used for short-term line holding and where long-term reliability is not so important. A cam cleat 10 such as shown in FIGS. 1-3 is typically used to temporarily hold a sheet (line for adjusting the force applied to a sail) or other control line. FIG. 1 shows cam cleat 10 in an idle position with no line cleated in it. FIG. 2 shows cleat 10 in an operating position with a line 30 cleated therein.
A cam cleat has a base 13 and, not surprisingly, at least one spring-loaded cam 18 mounted on base 13 for rotation about an axle 21 through a fraction of a complete turn. Cam 18 typically has an approximate cylindrical shape whose height along an axis of rotation 29 for cam 18 (see FIG. 3) may be perhaps half the largest transverse dimension. (The definition of cylinder used here is that from solid geometry as the locus of a line moving parallel to an axis to form a closed loop.) Cam 18 has a lower surface 26 adjacent to base 13 and an upper surface 25 opposite surface 26, to thereby define the volume of cam 18.
The spring loading for cam 18 is provided by a spring (not shown) that urges cam 18 in a counterclockwise direction around axle 21. A stop, also unshown, limits the counterclockwise rotation of cam 18 to approximately that shown in FIG. 1.
Cam 18 has a peripheral segment that is eccentrically mounted with respect to axle 21 and that forms a jaw 22. By “eccentrically mounted” here is meant that as cam 18 rotates about axle 21, jaw 22 swings into and out of a gripping path 28 extending along a side of cam 21. Line 30 extends along gripping path 28 when gripped by cam 18. Most often jaw 22 has a helical or spiral profile as seen in FIG. 2.
Jaw 22 is formed from a series of teeth 24 or other friction-enhancing feature that defines a gripping surface. The radial distance R for teeth 24 with respect to axle 21 increases with an increasing clockwise angle relative to axle 21. The use of a spiral profile allows cleat 10 to more easily accept a range of line diameters. The use of a plurality of teeth 24 to forming the gripping surface is typical and reduces wear on both the teeth 24 and line 30.
For some applications even a single eccentrically mounted tooth 24 forming jaw 22 on cam 18 will be sufficient to grip a line 30 and is to be included in the general definition of a cam cleat jaw 22. Of course such a single tooth cam does not have a spiral profile, but will still be generally referred to as a cam, for lack of a better term if for no other reason.
Prior art cam cleats usually have a second spring-loaded cam 19 having more or less a mirror image of clam 18. Cam 19 has a jaw 23 facing jaw 22 with the gripping path 28 running between them. The spring loading for cam 19 urges cam 19 in a clockwise direction.
In use, a line 30 is inserted between jaws 22 and 23 with a downward and backward (to the left in FIGS. 1 and 2) motion on segment 30b of line 30. Friction between line segment 30b and jaws 22 and 23 during this motion rotates cams 18 and 19 into an open position as shown in FIG. 2 allowing the downward force on line segment 30b to open cams 18 and 19 and line segment 30 to slip between jaws 22 and 23.
The spring loading creates friction between jaws 22 and 23 on the one hand and line 30 on the other. Tension T in segment 30a of line 30 as indicated by arrow 33 causes line 30 to slip slightly to the right, and the friction thus created to cause cam 18 to rotate counterclockwise slightly and cam 19 to rotate clockwise slightly. The eccentric mount of jaws 22 and 23 causes line 30 to be gripped and compressed between jaws 22 and 23 as shown in FIGS. 2 and 3. The gripping and compression limits slippage of line 30 within jaws 22 and 23 and essentially immobilizes line 30 in the direction of tension.
If tension on line 30 is high the gripping may create so much friction that line 30 cannot be easily removed from jaws 22 and 23 without releasing some of the tension that line 30 applies to cams 18 and 19. On the other hand, if line 30 tension is low, the gripping force may be so low that line 30 can easily be removed from jaws 22 and 23, perhaps even when not desired.
FIGS. 1-3 also show a fairlead 27 mounted at the opening of the jaws 22 and 23. Fairlead 27 straddles gripping path 28. Fairlead 27 serves two purposes. First, by tying a simple overhand or figure eight knot in line segment 30b that can't pass through fairlead 27, line 30 can be kept more or less permanently in position for cleating between cams 18 and 19 as needed. The knot and fairlead 27 also limit the amount of movement line 30 can undergo in the direction of the tension arrow 33.
Fairlead 27 also prevents cams 18 and 19 from releasing line 30 if the tension in line segment 30a is angled above the plane of base 13. A number of nautical situations can arise where the tension in segment 30a is directed above the plane of base 13, either temporarily or permanently. For example, if the cleat were to be used for temporarily mooring a craft to a dock, stepping on the bow might cause the bow to fall and the angle between line segment 30a and the base 13 plane to rise above the plane of base 13. The upward force component in line segment 30 may be sufficient to slip line 30 from cams 18 and 19 were it not for the fairlead 27 that keeps the angle of line segment 30 adjacent cams 18 and 19 more or less parallel to the base 13 plane.
However, a cam cleat 10 with a conventional fairlead 27 is somewhat inconvenient to use where a line is to be only temporarily clamped in the cleat. The line must first be led through fairlead 27, which takes extra time and more precise manipulation. A situation where line 30 is already under tension can often require two hands to cleat a line in a cam cleat with a fairlead 27 of the type shown. Nevertheless, a cam cleat with a fairlead is often very useful in nautical and other applications.